There are many types of electromagnetically operated devices or actuators which are currently used to control switch contacts and provide an open, closed, or changeover functionality. Typical examples of such devices include those which use the movement of the flexure or cantilever to open and/or close valves controlling a flow of fluid. Many such valves require a continuous electric current to hold the armature in one position or the other. This wastes energy and can produce unwanted heat. To avoid using a continuous flow of electric current, binary actuated valves have been developed such as that of the type disclosed in U.S. Pat. No. 6,935,373.
Existing binary valves of the type disclosed in U.S. Pat. No. 6,935,373 operate bi-stably in either the fully-open or fully-closed states, using permanent magnets to hold the valve in each state. To change the state of the valve, a single short electrical pulse is sent to the coil to reduce, remove, or reverse the attractive magnetic force, causing the valve to switch states with the help of a mechanical spring. Such a valve can be controlled using a pulse width modulation (PWM) transistor-transistor logic (TTL) signal, with an edge-detection circuit sending actuating pulses to the coil in response to the edges of the PWM signal.
In many applications, it is desirable to have valves that can pass large flow rates and switch with short time delays despite high pressure differentials across the seal. One such application is pneumatic control of truck brakes. In this application, it is desirable that valves have effective orifice diameters of up to 9 mm and switching times of 3 ms. Furthermore, pressure differentials across the valve can be up to 12.5 bar. This combination of performance parameters is not achievable with conventional valve technologies, which tend to have switching times longer than 15 ms.
Typical existing binary valves, such as that shown in FIG. 1, achieve switching times shorter than 4 ms with a 9 bar pressure differential, but only for effective orifice diameters smaller than 3.5 mm. Such performance is sufficient in applications where fast and small pressure adjustments are required. However, many applications require higher pressures, flow rates, and switching speeds.
The valve according to the present invention has been developed to overcome the limitations of previous binary valves, such that it would achieve specifications suitable for pneumatic brake actuation when placed directly on the brake chamber. This requires changes in the pressure in the chamber greater than 0.5 bar at 12.5 Hz with a supply pressure of 12.5 bar.